The present invention relates generally to control circuits and more particularly to such circuits for supplying a single pulse to actuate a load.
In the past, various circuitry was employed to effect actuation of single stroke, electrically operable, hand held tools, such as a fastener driving tool or the like. The art is replete with schemes which provided single energy pulses to actuate, for example, solenoid operated devices, such as electric typewriters, paper tape punches, fastener driving devices and the like. At least some of these schemes frequently employed an accumulated charge on a large storage capacitor as an energy source which actuated the solenoid with appropriate gating occurring upon command. Another approach frequently employed was to utilize a capacitor for triggering a silicon controlled rectifier to gate substantially a half cycle of an applied alternating current to the solenoid thereby to operate the device. A variation on some of these schemes was to employ two solenoids and to gate two consecutive half cycles of the alternating current sequentially to these two solenoids to provide a greater driving force for the tool or device. One of the disadvantageous or undesirable features of at least some of these trigger capacitor type schemes was that the firing of the silicon controlled rectifier did not adequately discharge the trigger capacitor, and accordingly, the circuit refired on a subsequent half cycle of like polarity. Such refiring, i.e. "doubling" or even "tripling", was in the least annoying and, in the case of fastener driving machinery that automatically reloaded itself between firings, might have been quite dangerous to the operator.